Recent studies indicated that diabetic autonomic neuropathy can lead to the long QT interval syndrome. This may increase the susceptibility of patients with diabetic autonomic neuropathy to ventricular arrhythmias and subsequent sudden death. The prevalence of and the risk factors for this condition will be determined in diabetic and non-diabetic Pima Indians by reviewing the electrocardiograms and the records of 1,000 adults seen at the NIH research clinic. In addition, 50 diabetic subjects with long Q-T interval, 50 diabetic subjects with normal Q-T interval, and 50 nondiabetic subjects with normal electrocardiograms will be studied in detail. All subjects will undergo detailed evaluation of the autonomic nervous system using a battery of standardized tests. Ambulatory cardiac monitoring will be obtained to determine the frequency of silent ischemic episodes and ventricular premature beats.